1. Field of the Invention:
The invention relates to a gas lift type pump for oil and gas wells which utilizes relatively low gas pressures existing in a well conduit to effect the elevation of liquids in the well conduit to the surface.
2. DESCRIPTION OF PRIOR ART:
Gas lift type pumps have long been utilized in subterranean wells where the natural pressure existing in the well is insufficient to produce a free flow of gas and liquids to the surface. Such prior art devices incorporated a plunger element which is slidably and sealably engaged with the well conduit, which may be either the well casing or a tubing string extending from the well surface to the body of liquid accumulated in the bottom of the conduit. The plunger defines a vertically extending, internal passage bypassing the external seal on the plunger element. A valve mechanism is provided within the body of the plunger and is effective to close the internal passage when the plunger has reached a preselected depth in the accumulated liquids where the hydrostatic pressure is sufficient to effect the movement of the valve to its closed position. With the valve closed, the natural gas existing in the well accumulates below the plunger and acts on the plunger as a piston to move the plunger and all liquids located above the plunger to the well surface. A typical pump of this type is shown in GRAMLING patent #4,070,134.
The prior art devices, such as the GRAMLING gas lift pump have suffered from several disadvantages. In the first place, the closing of the valve when the plunger reaches the preselected depth in the well liquids is not positively effected, so that the valve may chatter between an open and closed position and thereby substantially reduce the upwardly directed gas forces operating on the plunger to move it to the well surface. Additionally, when the valve does close, a special mechanism has to be provided at the well surface to reopen the valve to permit the plunger to again descend into the well. Lastly, since the force holding the valve in its open position is primarily derived from the weight of the valve, the valve will always close when it has reached a minimum level in the well liquids where the hydrostatic pressure on the valve slightly exceeds the weight of the valve. This is a substantial disadvantage where the gas pressure in the well is sufficient to move a greater column of liquid upwardly through the well conduit. Thus the prior art devices are not susceptible to ready adjustment to accommodate the specific pressures and liquid depths found in various wells.